Add chart empty state and home-page real-time price refresh

- Show "No price history available for this range yet." overlay when
  the caliber chart range contains no daily averages (previously the
  chart rendered as an unlabeled empty grid).
- Subscribe HomeLive to the "prices:updated" PubSub topic so the
  cheapest-per-caliber grid refreshes without a full page reload.
- Drop the unused textColor computation and unused max series from the
  chart hook/data.

lib/ammoprices_web/live/caliber_live/show.ex

@@ -181,11 +181,10 @@ defmodule AmmopricesWeb.CaliberLive.Show do
     chart_data = %{
       labels: Enum.map(daily_data, &Date.to_iso8601(&1.date)),
       avg: Enum.map(daily_data, & &1.avg_ppr),
-      min: Enum.map(daily_data, & &1.min_ppr),
-      max: Enum.map(daily_data, & &1.max_ppr)
+      min: Enum.map(daily_data, & &1.min_ppr)
     }
 
-    assign(socket, :chart_data, chart_data)
+    assign(socket, chart_data: chart_data, chart_empty?: daily_data == [])
   end
 
   defp load_price_stats(socket) do
@@ -279,14 +278,25 @@ defmodule AmmopricesWeb.CaliberLive.Show do
               </button>
             </div>
           </div>
-          <div
-            id="price-chart-container"
-            phx-hook=".PriceChart"
-            phx-update="ignore"
-            data-chart-data={Jason.encode!(@chart_data)}
-            class="h-64 sm:h-80"
-          >
-            <canvas id="price-chart" class="w-full h-full"></canvas>
+          <div class="relative h-64 sm:h-80">
+            <div
+              id="price-chart-container"
+              phx-hook=".PriceChart"
+              phx-update="ignore"
+              data-chart-data={Jason.encode!(@chart_data)}
+              class="w-full h-full"
+            >
+              <canvas id="price-chart" class="w-full h-full"></canvas>
+            </div>
+            <div
+              :if={@chart_empty?}
+              id="price-chart-empty"
+              class="absolute inset-0 flex items-center justify-center pointer-events-none"
+            >
+              <p class="text-sm text-base-content/40">
+                No price history available for this range yet.
+              </p>
+            </div>
           </div>
         </div>
 
@@ -504,10 +514,6 @@ defmodule AmmopricesWeb.CaliberLive.Show do
 
               const ctx = canvas.getContext("2d")
 
-              // Get CSS custom property values for theming
-              const style = getComputedStyle(document.documentElement)
-              const textColor = style.getPropertyValue("color") || "#666"
-
               return new Chart(ctx, {
                 type: "line",
                 data: {

lib/ammoprices_web/live/home_live.ex

@@ -16,9 +16,11 @@ defmodule AmmopricesWeb.HomeLive do
 
   @impl true
   def mount(_params, _session, socket) do
+    if connected?(socket) do
+      Phoenix.PubSub.subscribe(Ammoprices.PubSub, "prices:updated")
+    end
+
     calibers = Catalog.list_calibers()
-    cheapest = Prices.cheapest_per_caliber()
-    cheapest_map = Map.new(cheapest, fn r -> {r.caliber_id, r.min_ppr} end)
 
     grouped =
       calibers
@@ -28,12 +30,25 @@ defmodule AmmopricesWeb.HomeLive do
       end)
 
     {:ok,
-     assign(socket,
+     socket
+     |> assign(
        page_title: "AmmoCPR",
        categories: @categories,
-       calibers_by_category: grouped,
-       cheapest_map: cheapest_map
-     )}
+       calibers_by_category: grouped
+     )
+     |> assign_cheapest_map()}
+  end
+
+  @impl true
+  def handle_info({:prices_updated, _}, socket) do
+    {:noreply, assign_cheapest_map(socket)}
+  end
+
+  defp assign_cheapest_map(socket) do
+    cheapest_map =
+      Map.new(Prices.cheapest_per_caliber(), fn r -> {r.caliber_id, r.min_ppr} end)
+
+    assign(socket, :cheapest_map, cheapest_map)
   end
 
   @impl true

test/ammoprices_web/live/caliber_live/show_test.exs

@@ -182,6 +182,22 @@ defmodule AmmopricesWeb.CaliberLive.ShowTest do
       assert has_element?(view, "#filter-casing-steel")
     end
 
+    test "shows empty chart state when no data exists in range", %{conn: conn, caliber: caliber} do
+      {:ok, view, _html} = live(conn, "/calibers/#{caliber.slug}")
+
+      assert has_element?(view, "#price-chart-empty")
+    end
+
+    test "hides empty chart state when data exists in range", %{conn: conn, caliber: caliber, retailer: retailer} do
+      product = product_fixture(%{caliber: caliber, retailer: retailer, in_stock: true})
+      now = DateTime.truncate(DateTime.utc_now(), :second)
+      snapshot_fixture(%{product: product, price_per_round_cents: 28, in_stock: true, recorded_at: now})
+
+      {:ok, view, _html} = live(conn, "/calibers/#{caliber.slug}")
+
+      refute has_element?(view, "#price-chart-empty")
+    end
+
     test "chart container uses phx-update=ignore to survive DOM patches", %{
       conn: conn,
       caliber: caliber,

test/ammoprices_web/live/home_live_test.exs

@@ -33,5 +33,19 @@ defmodule AmmopricesWeb.HomeLiveTest do
 
       assert html =~ "25"
     end
+
+    test "updates cheapest prices via PubSub broadcast", %{conn: conn} do
+      caliber = caliber_fixture(%{name: "9mm Luger", slug: "9mm-luger", category: "handgun"})
+      retailer = retailer_fixture()
+      product = product_fixture(%{caliber: caliber, retailer: retailer, in_stock: true})
+      now = DateTime.truncate(DateTime.utc_now(), :second)
+
+      {:ok, view, _html} = live(conn, "/")
+
+      snapshot_fixture(%{product: product, price_per_round_cents: 17, in_stock: true, recorded_at: now})
+      Phoenix.PubSub.broadcast(Ammoprices.PubSub, "prices:updated", {:prices_updated, %{}})
+
+      assert render(view) =~ "0.17"
+    end
   end
 end